This invention relates to systems and methods for analyzing the vibrational behavior of composite mechanical structures, such as buildings, aircraft, machines, dams and the like.
Composite structures, such as buildings, aircraft, dams, machines and the like are designed to withstand either theoretically calculated or empirically determined maximum loads and stresses in the environment for which they are intended. However, the actual response of such structures to varying environmental conditions, such as wind stress, alteration of subsoil conditions, acceleration forces, and aging of the component structural elements, typically varies with time and catastrophic failure may occur unless the mechanical and structural characteristics are monitored. In the past, the continuing structural performance of composite structures has been monitored, if at all, primarily by means of linear displacement sensors, such as strain gauges, pressure transducers, accelerometers and the like, all of which respond only to linear motion. Further, such devices have typically been used to monitor only specific individual structural elements, such as wing struts in an aircraft or critical load beams in the case of buildings. In such prior art methods of monitoring the integrity of composite structures, the principal object has been to determine the loading or the deflection in the structural component to which the linear motion transducers have been attached. The chief disadvantage to such an approach lies in the fact that only the static characteristics of the individually monitored structural elements are placed under observation which, except in the case of an obvious fracture of a beam or other catastrophic failure, provides no information with respect to the dynamic response of the individual elements or the relative integrity of the remaining structural elements, whose failure could also cause impairment or total destruction of the composite structure. In addition, the use of linear motion sensors to detect structural characteristics suffers from the further disadvantages that such devices also detect noise or rigid body inertial motions, which must be somehow compensated for by electrical or mechanical filtering, thereby requiring relatively sophisticated electrical or mechanical circuits for this purpose. Moreover, most linear motion sensors require a local source of electrical power for proper operation, which is not always available at remote sensor locations without special wiring or the provision of independent battery operated power supplies. Further, many linear motion sensors have a mass of sufficient size as to alter the vibration characteristics of the structural element to which the device is attached, which not only renders calibration of the sensor more difficult, but also requires subjective interpolation of the vibrational response signals from the sensor.